Piston



P. L. BOWSER ETAL PISTON Filed May 16. was

2 Sheets-Sheet 2 INVENTORS 1 O Psncy L. Bewae'n, WILLIAM MVG/VNER, 4m: PEncy L. BowsER,dR.

ATTORNEYS PISTON Percy L. Bowser, University City, William M.- -Venner, Richmond Heights, and Percy L. Bowser, Jr., University City, Mo., assignors to The Sterling Corporation, St. Louis, Mo., a corporation of Delaware Application May 1c, 1938, Serial No. 208,134

2' Claims.

This invention pertains to trunk pistons such as are used in internal combustion engines and more particularly the pistons constructed of light metals such as aluminum, magnesium and alloys thereof.

One of the objects of this invention is to provicle a. piston of novel structure having means for restraining the thermal expansion thereof in the direction oi the piston diameter.

Another objectis to provide a light metal piston oi this type having means of a. lower coemcient of expansion applied in such a manner as to restrain expansion of the skirt diameter.

Another object is to provide novel means whereby the expansion of the piston head may he applied through connecting means to restrain expansion of the piston skirt.

Further objects will appear from the following description taken in connection with the accompanying drawings in which- Figure 1 is a longitudinal section of a piston embodying this invention.

Figure 2 is a side, view of the same showing one of the bearing sections thereof. v

Figure 3 is a side view taken from the end of the wrist pin axis".

Figure 4 is a longitudinal section. taken transversely of the wrist pin axis.

Figure 5 is a halt section taken transversely of the piston through the wrist pin axis.

Figure 6 is aside view taken along the wrist pin axis of a'piston. illustrating another embodiment of this invention.

Said connectors may be stiffened by reeniorcing ribs 8 extending therealong.

In the embodiment illustrated in Figures .1 to-5, inclusive, the two hearing sections 4 are formed separate from the connectors 6 by providing intervening gaps 9. An expansion controlling element in the form of a flexible band Figure '1 is a longitudinal half section along I the wrist pin axis of the piston of Figure 6.

Figure 8 is a longitudinal section of the same taken transversely to the wrist pin axis.

Figure 9 is a transverse section or the same taken on line 9-9 of Figure *ljj'iand Figure 10 i'sa developed view or the control ling element or band of the piston of Figure 6.

Referring to the drawings, the piston illustrated is of the trunk type havinga head I' and tilt skirt indicated generally at 2.. The skirt may considered as comprising-a lower clroum ferential rim 3 from which cylinder bearing sections 4 extend upwardly toward the piston head.

The bearing sections 4 are each separated from V the head I by ja horizontal slot 5' which may be cast in the piston but which is usually formed by a saw cut after the piston has been cast. A

pair of piers or connectors 6 extend downwardly.

irom the head, integrally connecting the head with the skirt, and with wrist pin bosses I formed at the lower ends of said piers or connectors.

I0 is arranged to connect the sections 4 with the connectorsfi. In Figures 1 to 5, this band is shown as a complete hoop extending around the interior or the skirt and cast into the outer portions of the bosses l, as shown in Figure 5, and into the middle portion only of the sections 4. The connection of the band III to the sections 4 may be made by means of a narrow internal rib ll extending along the middle portion only of the sections 4 and having portions ofthe cast metal extending through openings in the band 10 as indicated at I2 in order to provide a secure connection between the band and the cast metal.

The band It is preferably constructed of me.-

I terial having av lower co-eflicient or thermal expansion than that or the piston metal. It has been found that for an aluminum piston, a band of steel provides a satisfactory controlling member. As shown in Figure 5, this band extends around the interior of the shirt in a nearly clrcular form and is imbedded in the bosses I as near their outer ends as possible.

In the embodiment shown in Figures 6 to '10, only one of the bearing sections 4' is "formed separate from the connectors i, the other sec tion being integrally connected with the piers or connectors so as to be rigidly supported there'- by. In this embodiment, the control member shown at i0 is arranged to form approximately a semi-circle extending around that side of the skirt on which the bearing sectionflis separate irom the connectors 6. In this embiiiment the band may be provided with openings or notches I2 adapted to receive the cast metal II. The

, ends or the band may be recessed as indicated at i3 where they are imbedded in the bosses .l. so as to surroundthe wrist pin"opening. The

ends ll of the band may be bent inwardly, as shown in Figure 9, so as to provide a secure inter-lock where they are imbedded in the bosses I. These, ends may be arranged to project in,- wardly from the castingto a slight extent, the

projecting ends being set into shiftable receiving cast solid with the head, that is, without the slot 5. When the casting cools, the contraction of the piston metal is usually greater than that of the band in. Furthermore, the metal of the skirt usually sets somewhat before the metal of the head becomes solid so that there is a lag in the cooling temperature of the head behind that of the skirt. As a consequence the head contracts after the skirt has solidified and, accordingly, there is an inward tension placed upon the skirt by the contraction of the head. Since the band I is within the skirt, it is subjected to compression during such cooling. When now the slot is cut, the skirt is freed from the head and springs outwardly with respect thereto on account of the release of this inward tension. This action tends to produce aslight clearance between the skirt section 4i and the band it) at the points indicated by the numeral l5. Accordingly, the section 4 is supported at its middle portion and relatively free at its side edges so that it may twist or warp to a certain extent in order to accommodate itself to the pressure of the cylinder wall.

The outer bearing surface of the skirtmay be machined to a slightly oval form with the minor axis of the oval in a direction parallel to the wrist pin axis. The skirt surface may also be relieved in the regions of the ends of the bosses I, as indicated at I6. This piston may be given a fairly snug fit in the cylinder across the diameteriof the faces 4. A clearance as small as one-thousandth of an inch on the diameter has been used successfully. When the piston is in service, the heat of combustion is applied to the piston head and transmitted therefrom to the skirt. The head usually expands to a greater extent than the skirt. This expansion of the head carries with it the connectors 6 and the bosses 1 to the outer portion of which the band) or i0 is connected. Such expansion of the bosses, therefore, tends to stretch the band along the wrist pin axis and therefore to contract its diameter on the transverse axis. This causes the band to exert a tension upon the skirt sections 4 connected thereto so as to draw them inwardly and compensate for the tendency of these portions of the skirt to expand radially. By proper adjustment, this tendency can be compensated almost exactly so that a uniform fit of the skirt in the cylinder may be maintained. It will be noted that on account of the springing out of the sections 4, as described above, the band curvature is slightly increased at the point of connection to the section 4. Furthermore, since the point of connection of the band to the bosses 1 is at their outer portion, the maximum expansion along the wrist pin axis is efiec tive to stretch the band, and since the portions thereof intervening between the bosses and the connecting point to the sections 4 are nearly straight, the stretching thereof acts with a sort oftoggle action to draw inwardly the skirt sections 4.

It will be seen, therefore, that a piston struc- I inder in which it operates is corrected by providing a control member of a less co-efiicient of expansion connected so that the expansion along the wrist pin axis is applied through this member to restrain expansion of the skirt along the transverse axis.

While a certain theory of operation has been set forth above, it will be understood that this is for the purpose of clarity in explanation and that it is not intended to set up any particular theory of operation as a basis for this invention. It is further understood that various individual features or sub-combinations of the piston, as illustrated and described, may be found useful by themselves without reference to other features or the complete combination, and the employment of such individual features or subcombinations is contemplated by this invention and within the scope of the appended claims.

It is further obvious that changes may be made in the details of construction within the scope of the appended claims without departing from the spirit of this invention; it is understood, therefore, that the invention is not limited to the specific details shown and described.

Having thus described the invention, what is claimed is:

1. A trunk piston of the character described having a head and a skirt, wrist-pin bosses on said skirt, rigid coonnectors joining said head integrally to said skirt and said bosses, said skirt having cylinder-bearing sections in the regions between said bosses one of which sections is integrally connected with said bosses while the other is separate therefrom, both of said sections being separated from said head, said head and skirt being constructed of a material having a high coefiicient of thermal expansion, and a flexible band of material having a lower coeflicient of thermal expansion anchored to the outer portions of said bosses and connected to the middle portion only of said separate cylinderbearing section in order to transmit thereto expansion of said bosses in a direction such as to restrain expansion of said section.

2. A trunk piston, comprising, a head, a skirt, wrist-pin bosses, connectors integrally connecting said skirt and said bosses with said head, said skirt having cylinder-bearing sections in the regions between said bosses, said sections being separated from said head and one of said sections being separate from said connectors, said head and skirt being constructed of material having a high coefficient of thermal expansion, and a flexible band of material having a lower coefficient of thermal expansion anchored to the outer portions of said bosses and connected to the middle portion only of said separate section in order to transmit thereto expansion of said bosses in a direction such as to restrain expansion of said section, said band lying wholly inwardly of said section except at the connection thereof, and being formed with a greater curvature than said section.

PERCY L. BOWSER. WILLIAM M. VENNER. PERCY L. BOWSER, JR. 

